Thermally Stable Red‐Emitting Mixed Halide Perovskite Nanocrystals Enabled by Solid Reaction and Co‐Doping Process

Abstract Rapid performance degradation as temperature increases for metal halide perovskite nanocrystals (NCs) greatly restricts the practical application for lighting and display. This problem is even more grievous for the mixed‐halide perovskite NCs because of severe ions migration. Here, a solid‐reaction process in the N₂ atmosphere is devised, in which the red‐emitting (631 nm wavelength) mixed halide CsPbBr_1.5I_1.5 NCs with a coating of SiO₂ shell are achieved. Meanwhile, the Zn²⁺ and K⁺ ions are co‐doped into the crystal lattice to enhance the radiative decay rate and decrease the trap density of the NCs. The photoluminescence quantum yield of the co‐doped NCs reaches 64.5%, which is one of the highest values for the reported mixed‐halide perovskite NCs obtained by the solid reaction. Importantly, the dopant of K⁺ enters into the interstitial position of the perovskite structure to increase the structural rigidity, which inhibits exciton–phonon interaction and elevates thermal activation energy, thus improving thermal quenching resistance to sustain high emission intensity at high temperature (>353 K). Furthermore, the red backlight emitting diode based on the NCs exhibits no decay in luminescence intensity after continuous operation for 700 h at 353 K, representing remarkable stability for the commercial application.